CONICET | Buscador de Institutos y Recursos Humanos

Studying the controls on biomass allocation trade-offs in plants are important since they affect harvestable product yields and are critical to understanding symbioticinteractions. Epichloae fungal endophytes associate with cool-season grasses, growing systemically within the plant inter-cellular spaces and are transmitted through seeds. We explore the endophytes influence on the relationship between the plant reproductive and vegetative aboveground biomass (reproductive effort: RE) and on the trade-off betweentwo components of the reproductive biomass, number and weight of panicles (RPN), using tall fescue as a model system. Naturally endophyte-colonized, manipulativelyendophyte-free, and naturally endophyte-free plants from Northern European wild-populations together with the cultivar Kentucky-31 were grown under different environmental conditions (nutrients x water). The endophyte had an effect on the RPN (E+: 6.19, ME-: 4.68 and E-: 4.40) which indicates how reproductive biomass is partitioned into number and mass of panicles, but not on RE (≈0.06). As expected, wild plants showed higher reproductive effort (≈0.06) compared to the cultivar KY-31 (0.05), irrespectiveof endophyte presence. Endophyte-colonized plants had lighter panicles than endophyte-free plants, a pattern that was clear among low-yielding plants. Similarly, the tradeoff between RPN and RE was higher for endophytecolonized plants. This was again evident among plants with low RE indicating that colonized plants split the yield into either greater number of panicles and/or lighter panicles. The effect of vertically transmitted endophytes has earlier been studied as ratios (e.g. RE); however, our study shows that this approach may hide size-dependent endophyte effects on these relationships. Our study reveals thatNeotyphodium endophyte affects trade-offs in tall fescue plants in a complex manner, and is influenced by a number of biological and abiotic factors.

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